theory Spec

  imports Main "~~/src/HOL/Library/Sublist"

begin

section {* Sequential Composition of Languages *}

definition

  Sequ :: "string set \<Rightarrow> string set \<Rightarrow> string set" ("_ ;; _" [100,100] 100)

where 

  "A ;; B = {s1 @ s2 | s1 s2. s1 \<in> A \<and> s2 \<in> B}"

text {* Two Simple Properties about Sequential Composition *}

lemma Sequ_empty_string [simp]:

  shows "A ;; {[]} = A"

  and   "{[]} ;; A = A"

by (simp_all add: Sequ_def)

lemma Sequ_empty [simp]:

  shows "A ;; {} = {}"

  and   "{} ;; A = {}"

by (simp_all add: Sequ_def)

section {* Semantic Derivative (Left Quotient) of Languages *}

definition

  Der :: "char \<Rightarrow> string set \<Rightarrow> string set"

where

  "Der c A \<equiv> {s. c # s \<in> A}"

definition

  Ders :: "string \<Rightarrow> string set \<Rightarrow> string set"

where

  "Ders s A \<equiv> {s'. s @ s' \<in> A}"

lemma Der_null [simp]:

  shows "Der c {} = {}"

unfolding Der_def

by auto

lemma Der_empty [simp]:

  shows "Der c {[]} = {}"

unfolding Der_def

by auto

lemma Der_char [simp]:

  shows "Der c {[d]} = (if c = d then {[]} else {})"

unfolding Der_def

by auto

lemma Der_union [simp]:

  shows "Der c (A \<union> B) = Der c A \<union> Der c B"

unfolding Der_def

by auto

lemma Der_Sequ [simp]:

  shows "Der c (A ;; B) = (Der c A) ;; B \<union> (if [] \<in> A then Der c B else {})"

unfolding Der_def Sequ_def

by (auto simp add: Cons_eq_append_conv)

section {* Kleene Star for Languages *}

inductive_set

  Star :: "string set \<Rightarrow> string set" ("_\<star>" [101] 102)

  for A :: "string set"

where

  start[intro]: "[] \<in> A\<star>"

| step[intro]:  "\<lbrakk>s1 \<in> A; s2 \<in> A\<star>\<rbrakk> \<Longrightarrow> s1 @ s2 \<in> A\<star>"

(* Arden's lemma *)

lemma Star_cases:

  shows "A\<star> = {[]} \<union> A ;; A\<star>"

unfolding Sequ_def

by (auto) (metis Star.simps)

lemma Star_decomp: 

  assumes "c # x \<in> A\<star>" 

  shows "\<exists>s1 s2. x = s1 @ s2 \<and> c # s1 \<in> A \<and> s2 \<in> A\<star>"

using assms

by (induct x\<equiv>"c # x" rule: Star.induct) 

   (auto simp add: append_eq_Cons_conv)

lemma Star_Der_Sequ: 

  shows "Der c (A\<star>) \<subseteq> (Der c A) ;; A\<star>"

unfolding Der_def Sequ_def

by(auto simp add: Star_decomp)

lemma Der_star [simp]:

  shows "Der c (A\<star>) = (Der c A) ;; A\<star>"

proof -    

  have "Der c (A\<star>) = Der c ({[]} \<union> A ;; A\<star>)"  

    by (simp only: Star_cases[symmetric])

  also have "... = Der c (A ;; A\<star>)"

    by (simp only: Der_union Der_empty) (simp)

  also have "... = (Der c A) ;; A\<star> \<union> (if [] \<in> A then Der c (A\<star>) else {})"

    by simp

  also have "... =  (Der c A) ;; A\<star>"

    using Star_Der_Sequ by auto

  finally show "Der c (A\<star>) = (Der c A) ;; A\<star>" .

qed

section {* Regular Expressions *}

datatype rexp =

  ZERO

| ONE

| CHAR char

| SEQ rexp rexp

| ALT rexp rexp

| STAR rexp

section {* Semantics of Regular Expressions *}

fun

  L :: "rexp \<Rightarrow> string set"

where

  "L (ZERO) = {}"

| "L (ONE) = {[]}"

| "L (CHAR c) = {[c]}"

| "L (SEQ r1 r2) = (L r1) ;; (L r2)"

| "L (ALT r1 r2) = (L r1) \<union> (L r2)"

| "L (STAR r) = (L r)\<star>"

section {* Nullable, Derivatives *}

fun

 nullable :: "rexp \<Rightarrow> bool"

where

  "nullable (ZERO) = False"

| "nullable (ONE) = True"

| "nullable (CHAR c) = False"

| "nullable (ALT r1 r2) = (nullable r1 \<or> nullable r2)"

| "nullable (SEQ r1 r2) = (nullable r1 \<and> nullable r2)"

| "nullable (STAR r) = True"

fun

 der :: "char \<Rightarrow> rexp \<Rightarrow> rexp"

where

  "der c (ZERO) = ZERO"

| "der c (ONE) = ZERO"

| "der c (CHAR d) = (if c = d then ONE else ZERO)"

| "der c (ALT r1 r2) = ALT (der c r1) (der c r2)"

| "der c (SEQ r1 r2) = 

     (if nullable r1

      then ALT (SEQ (der c r1) r2) (der c r2)

      else SEQ (der c r1) r2)"

| "der c (STAR r) = SEQ (der c r) (STAR r)"

fun 

 ders :: "string \<Rightarrow> rexp \<Rightarrow> rexp"

where

  "ders [] r = r"

| "ders (c # s) r = ders s (der c r)"

lemma nullable_correctness:

  shows "nullable r  \<longleftrightarrow> [] \<in> (L r)"

by (induct r) (auto simp add: Sequ_def) 

lemma der_correctness:

  shows "L (der c r) = Der c (L r)"

by (induct r) (simp_all add: nullable_correctness)

lemma ders_correctness:

  shows "L (ders s r) = Ders s (L r)"

by (induct s arbitrary: r)

   (simp_all add: Ders_def der_correctness Der_def)

section {* Values *}

datatype val = 

  Void

| Char char

| Seq val val

| Right val

| Left val

| Stars "val list"

section {* The string behind a value *}

fun 

  flat :: "val \<Rightarrow> string"

where

  "flat (Void) = []"

| "flat (Char c) = [c]"

| "flat (Left v) = flat v"

| "flat (Right v) = flat v"

| "flat (Seq v1 v2) = (flat v1) @ (flat v2)"

| "flat (Stars []) = []"

| "flat (Stars (v#vs)) = (flat v) @ (flat (Stars vs))" 

abbreviation

  "flats vs \<equiv> concat (map flat vs)"

lemma flat_Stars [simp]:

 "flat (Stars vs) = flats vs"

by (induct vs) (auto)

lemma Star_concat:

  assumes "\<forall>s \<in> set ss. s \<in> A"  

  shows "concat ss \<in> A\<star>"

using assms by (induct ss) (auto)

lemma Star_cstring:

  assumes "s \<in> A\<star>"

  shows "\<exists>ss. concat ss = s \<and> (\<forall>s \<in> set ss. s \<in> A \<and> s \<noteq> [])"

using assms

apply(induct rule: Star.induct)

apply(auto)[1]

apply(rule_tac x="[]" in exI)

apply(simp)

apply(erule exE)

apply(clarify)

apply(case_tac "s1 = []")

apply(rule_tac x="ss" in exI)

apply(simp)

apply(rule_tac x="s1#ss" in exI)

apply(simp)

done

section {* Lexical Values *}

inductive 

  Prf :: "val \<Rightarrow> rexp \<Rightarrow> bool" ("\<Turnstile> _ : _" [100, 100] 100)

where

 "\<lbrakk>\<Turnstile> v1 : r1; \<Turnstile> v2 : r2\<rbrakk> \<Longrightarrow> \<Turnstile>  Seq v1 v2 : SEQ r1 r2"

| "\<Turnstile> v1 : r1 \<Longrightarrow> \<Turnstile> Left v1 : ALT r1 r2"

| "\<Turnstile> v2 : r2 \<Longrightarrow> \<Turnstile> Right v2 : ALT r1 r2"

| "\<Turnstile> Void : ONE"

| "\<Turnstile> Char c : CHAR c"

| "\<forall>v \<in> set vs. \<Turnstile> v : r \<and> flat v \<noteq> [] \<Longrightarrow> \<Turnstile> Stars vs : STAR r"

inductive_cases Prf_elims:

  "\<Turnstile> v : ZERO"

  "\<Turnstile> v : SEQ r1 r2"

  "\<Turnstile> v : ALT r1 r2"

  "\<Turnstile> v : ONE"

  "\<Turnstile> v : CHAR c"

  "\<Turnstile> vs : STAR r"

lemma Prf_Stars_appendE:

  assumes "\<Turnstile> Stars (vs1 @ vs2) : STAR r"

  shows "\<Turnstile> Stars vs1 : STAR r \<and> \<Turnstile> Stars vs2 : STAR r" 

using assms

by (auto intro: Prf.intros elim!: Prf_elims)

lemma Star_cval:

  assumes "\<forall>s\<in>set ss. \<exists>v. s = flat v \<and> \<Turnstile> v : r"

  shows "\<exists>vs. flats vs = concat ss \<and> (\<forall>v\<in>set vs. \<Turnstile> v : r \<and> flat v \<noteq> [])"

using assms

apply(induct ss)

apply(auto)

apply(rule_tac x="[]" in exI)

apply(simp)

apply(case_tac "flat v = []")

apply(rule_tac x="vs" in exI)

apply(simp)

apply(rule_tac x="v#vs" in exI)

apply(simp)

done

lemma L_flat_Prf1:

  assumes "\<Turnstile> v : r" 

  shows "flat v \<in> L r"

using assms

by (induct) (auto simp add: Sequ_def Star_concat)

lemma L_flat_Prf2:

  assumes "s \<in> L r" 

  shows "\<exists>v. \<Turnstile> v : r \<and> flat v = s"

using assms

proof(induct r arbitrary: s)

  case (STAR r s)

  have IH: "\<And>s. s \<in> L r \<Longrightarrow> \<exists>v. \<Turnstile> v : r \<and> flat v = s" by fact

  have "s \<in> L (STAR r)" by fact

  then obtain ss where "concat ss = s" "\<forall>s \<in> set ss. s \<in> L r \<and> s \<noteq> []"

  using Star_cstring by auto  

  then obtain vs where "flats vs = s" "\<forall>v\<in>set vs. \<Turnstile> v : r \<and> flat v \<noteq> []"

  using IH Star_cval by metis 

  then show "\<exists>v. \<Turnstile> v : STAR r \<and> flat v = s"

  using Prf.intros(6) flat_Stars by blast

next 

  case (SEQ r1 r2 s)

  then show "\<exists>v. \<Turnstile> v : SEQ r1 r2 \<and> flat v = s"

  unfolding Sequ_def L.simps by (fastforce intro: Prf.intros)

next

  case (ALT r1 r2 s)

  then show "\<exists>v. \<Turnstile> v : ALT r1 r2 \<and> flat v = s"

  unfolding L.simps by (fastforce intro: Prf.intros)

qed (auto intro: Prf.intros)

lemma L_flat_Prf:

  shows "L(r) = {flat v | v. \<Turnstile> v : r}"

using L_flat_Prf1 L_flat_Prf2 by blast

section {* Sets of Lexical Values *}

text {*

  Shows that lexical values are finite for a given regex and string.

*}

definition

  LV :: "rexp \<Rightarrow> string \<Rightarrow> val set"

where  "LV r s \<equiv> {v. \<Turnstile> v : r \<and> flat v = s}"

lemma LV_simps:

  shows "LV ZERO s = {}"

  and   "LV ONE s = (if s = [] then {Void} else {})"

  and   "LV (CHAR c) s = (if s = [c] then {Char c} else {})"

  and   "LV (ALT r1 r2) s = Left ` LV r1 s \<union> Right ` LV r2 s"

unfolding LV_def

by (auto intro: Prf.intros elim: Prf.cases)

abbreviation

  "Prefixes s \<equiv> {s'. prefixeq s' s}"

abbreviation

  "Suffixes s \<equiv> {s'. suffixeq s' s}"

abbreviation

  "SSuffixes s \<equiv> {s'. suffix s' s}"

lemma Suffixes_cons [simp]:

  shows "Suffixes (c # s) = Suffixes s \<union> {c # s}"

by (auto simp add: suffixeq_def Cons_eq_append_conv)

lemma finite_Suffixes: 

  shows "finite (Suffixes s)"

by (induct s) (simp_all)

lemma finite_SSuffixes: 

  shows "finite (SSuffixes s)"

proof -

  have "SSuffixes s \<subseteq> Suffixes s"

   unfolding suffix_def suffixeq_def by auto

  then show "finite (SSuffixes s)"

   using finite_Suffixes finite_subset by blast

qed

lemma finite_Prefixes: 

  shows "finite (Prefixes s)"

proof -

  have "finite (Suffixes (rev s))" 

    by (rule finite_Suffixes)

  then have "finite (rev ` Suffixes (rev s))" by simp

  moreover

  have "rev ` (Suffixes (rev s)) = Prefixes s"

  unfolding suffixeq_def prefixeq_def image_def

   by (auto)(metis rev_append rev_rev_ident)+

  ultimately show "finite (Prefixes s)" by simp

qed

lemma LV_STAR_finite:

  assumes "\<forall>s. finite (LV r s)"

  shows "finite (LV (STAR r) s)"

proof(induct s rule: length_induct)

  fix s::"char list"

  assume "\<forall>s'. length s' < length s \<longrightarrow> finite (LV (STAR r) s')"

  then have IH: "\<forall>s' \<in> SSuffixes s. finite (LV (STAR r) s')"

    by (auto simp add: suffix_def) 

  def f \<equiv> "\<lambda>(v, vs). Stars (v # vs)"

  def S1 \<equiv> "\<Union>s' \<in> Prefixes s. LV r s'"

  def S2 \<equiv> "\<Union>s2 \<in> SSuffixes s. Stars -` (LV (STAR r) s2)"

  have "finite S1" using assms

    unfolding S1_def by (simp_all add: finite_Prefixes)

  moreover 

  with IH have "finite S2" unfolding S2_def

    by (auto simp add: finite_SSuffixes inj_on_def finite_vimageI)

  ultimately 

  have "finite ({Stars []} \<union> f ` (S1 \<times> S2))" by simp

  moreover 

  have "LV (STAR r) s \<subseteq> {Stars []} \<union> f ` (S1 \<times> S2)" 

  unfolding S1_def S2_def f_def

  unfolding LV_def image_def prefixeq_def suffix_def

  apply(auto elim: Prf_elims)

  apply(erule Prf_elims)

  apply(auto)

  apply(case_tac vs)

  apply(auto intro: Prf.intros)

  done  

  ultimately

  show "finite (LV (STAR r) s)" by (simp add: finite_subset)

qed  

lemma LV_finite:

  shows "finite (LV r s)"

proof(induct r arbitrary: s)

  case (ZERO s) 

  show "finite (LV ZERO s)" by (simp add: LV_simps)

next

  case (ONE s)

  show "finite (LV ONE s)" by (simp add: LV_simps)

next

  case (CHAR c s)

  show "finite (LV (CHAR c) s)" by (simp add: LV_simps)

next 

  case (ALT r1 r2 s)

  then show "finite (LV (ALT r1 r2) s)" by (simp add: LV_simps)

next 

  case (SEQ r1 r2 s)

  def f \<equiv> "\<lambda>(v1, v2). Seq v1 v2"

  def S1 \<equiv> "\<Union>s' \<in> Prefixes s. LV r1 s'"

  def S2 \<equiv> "\<Union>s' \<in> Suffixes s. LV r2 s'"

  have IHs: "\<And>s. finite (LV r1 s)" "\<And>s. finite (LV r2 s)" by fact+

  then have "finite S1" "finite S2" unfolding S1_def S2_def

    by (simp_all add: finite_Prefixes finite_Suffixes)

  moreover

  have "LV (SEQ r1 r2) s \<subseteq> f ` (S1 \<times> S2)"

    unfolding f_def S1_def S2_def 

    unfolding LV_def image_def prefixeq_def suffixeq_def

    by (auto elim: Prf.cases)

  ultimately 

  show "finite (LV (SEQ r1 r2) s)"

    by (simp add: finite_subset)

next

  case (STAR r s)

  then show "finite (LV (STAR r) s)" by (simp add: LV_STAR_finite)

qed

section {* Our POSIX Definition *}

inductive 

  Posix :: "string \<Rightarrow> rexp \<Rightarrow> val \<Rightarrow> bool" ("_ \<in> _ \<rightarrow> _" [100, 100, 100] 100)

where

  Posix_ONE: "[] \<in> ONE \<rightarrow> Void"

| Posix_CHAR: "[c] \<in> (CHAR c) \<rightarrow> (Char c)"

| Posix_ALT1: "s \<in> r1 \<rightarrow> v \<Longrightarrow> s \<in> (ALT r1 r2) \<rightarrow> (Left v)"

| Posix_ALT2: "\<lbrakk>s \<in> r2 \<rightarrow> v; s \<notin> L(r1)\<rbrakk> \<Longrightarrow> s \<in> (ALT r1 r2) \<rightarrow> (Right v)"

| Posix_SEQ: "\<lbrakk>s1 \<in> r1 \<rightarrow> v1; s2 \<in> r2 \<rightarrow> v2;

    \<not>(\<exists>s\<^sub>3 s\<^sub>4. s\<^sub>3 \<noteq> [] \<and> s\<^sub>3 @ s\<^sub>4 = s2 \<and> (s1 @ s\<^sub>3) \<in> L r1 \<and> s\<^sub>4 \<in> L r2)\<rbrakk> \<Longrightarrow> 

    (s1 @ s2) \<in> (SEQ r1 r2) \<rightarrow> (Seq v1 v2)"

| Posix_STAR1: "\<lbrakk>s1 \<in> r \<rightarrow> v; s2 \<in> STAR r \<rightarrow> Stars vs; flat v \<noteq> [];

    \<not>(\<exists>s\<^sub>3 s\<^sub>4. s\<^sub>3 \<noteq> [] \<and> s\<^sub>3 @ s\<^sub>4 = s2 \<and> (s1 @ s\<^sub>3) \<in> L r \<and> s\<^sub>4 \<in> L (STAR r))\<rbrakk>

    \<Longrightarrow> (s1 @ s2) \<in> STAR r \<rightarrow> Stars (v # vs)"

| Posix_STAR2: "[] \<in> STAR r \<rightarrow> Stars []"

inductive_cases Posix_elims:

  "s \<in> ZERO \<rightarrow> v"

  "s \<in> ONE \<rightarrow> v"

  "s \<in> CHAR c \<rightarrow> v"

  "s \<in> ALT r1 r2 \<rightarrow> v"

  "s \<in> SEQ r1 r2 \<rightarrow> v"

  "s \<in> STAR r \<rightarrow> v"

lemma Posix1:

  assumes "s \<in> r \<rightarrow> v"

  shows "s \<in> L r" "flat v = s"

using assms

by (induct s r v rule: Posix.induct)

   (auto simp add: Sequ_def)

text {*

  Our Posix definition determines a unique value.

*}

lemma Posix_determ:

  assumes "s \<in> r \<rightarrow> v1" "s \<in> r \<rightarrow> v2"

  shows "v1 = v2"

using assms

proof (induct s r v1 arbitrary: v2 rule: Posix.induct)

  case (Posix_ONE v2)

  have "[] \<in> ONE \<rightarrow> v2" by fact

  then show "Void = v2" by cases auto

next 

  case (Posix_CHAR c v2)

  have "[c] \<in> CHAR c \<rightarrow> v2" by fact

  then show "Char c = v2" by cases auto

next 

  case (Posix_ALT1 s r1 v r2 v2)

  have "s \<in> ALT r1 r2 \<rightarrow> v2" by fact

  moreover

  have "s \<in> r1 \<rightarrow> v" by fact

  then have "s \<in> L r1" by (simp add: Posix1)

  ultimately obtain v' where eq: "v2 = Left v'" "s \<in> r1 \<rightarrow> v'" by cases auto 

  moreover

  have IH: "\<And>v2. s \<in> r1 \<rightarrow> v2 \<Longrightarrow> v = v2" by fact

  ultimately have "v = v'" by simp

  then show "Left v = v2" using eq by simp

next 

  case (Posix_ALT2 s r2 v r1 v2)

  have "s \<in> ALT r1 r2 \<rightarrow> v2" by fact

  moreover

  have "s \<notin> L r1" by fact

  ultimately obtain v' where eq: "v2 = Right v'" "s \<in> r2 \<rightarrow> v'" 

    by cases (auto simp add: Posix1) 

  moreover

  have IH: "\<And>v2. s \<in> r2 \<rightarrow> v2 \<Longrightarrow> v = v2" by fact

  ultimately have "v = v'" by simp